On Thu, 2010-05-27 at 07:50 +0100, Al Viro wrote:
> Note, e.g., that in your series you've touched udf; it can set s_dirt
> until the cows come home, but without ->write_super() it'll be ignored
> by everything in VFS and fs/udf itself never looks at the damn thing.
>
> A look around it shows fs/sysv, where we never clean the damn flag anymore
> for r/w mounts. Yes, really (got broken a year ago, nobody noticed).
>
> Or, e.g., BFS - there we have ->write_super() mark the buffer_head that
> contains on-disk sb dirty, and the only place that sets ->s_dirt is doing
> that immediately after having marked the same bh dirty itself. Interesting
> place, at that - bfs_fill_super() at r/w mount time... Note that ->sync_fs()
> there does *not* wait for anything, which is not the right thing to do.
>
> IOW, this thing is a good topic for code review; I suspect that quite a few
> users might be gone as the result.
Al,
you requested me to review s_dirt usage, well, I'm trying now. One thing
I do not understand is s_dirt serialization, which seems to be just
absent in some FSes. I checked affs and ext2. E.g., affs does:
affs_alloc_block()
{
mark_buffer_dirty(bh);
sb->s_dirt = 1;
}
vs
affs_write_super()
{
affs_commit_super();
/* YYY: what if sb is marked as dirty right here? */
sb->s_dirt = 0;
}
vs
/* This wakes up periodically */
sync_super()
{
if (sb->s_root && sb->s_dirt)
sb->s_op->write_super(sb);
}
ext2 seems to be doing something similar. It seems to me that FSes
should serialize s_dirt changes somehow, but they don't? Why this is not
a problem?
--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
